Glass envelope for electric sun lamps



Jan. 23, 194-5. 5 N ETAL 2,367,871

GLASS ENVELOPE FOR ELECTRIC SUNLAMPS Filed March 16, 1942 Transmission e1icincg.

Wavelength in millirnicrons;

lnvenfovs: Harrg ldaLsing, Hermann Krefi k,

K Fk Lavch'e, bgbz fl WM Their Ai kor'neg.

Faiienteddan. 23, E945 Harry liaising, Weisswasser, Hermann Kreflt,

EerlimSchoneberg, and Kurt Larch, Berlin- Tempelhof, Germany, assignors to General Electric Company, a corporation of New York Application March 16, 1942, Serial No. 434,973 In Germany December 22, 1939 2 Claims.

Our invention relates to sunlamps especially rich in ultraviolet radiation and more particularly to the glass envelopes of that type of ultraviolet electric sunlamp which is designed generally for nonprofessional use such as for general body exposure to improve the general health or-for cosmetic purposes.

In lampsof the aforesaid type it is highly desirable to employ a glass envelope which will.

absorb as much as possible the bodily harmful strong radiations of the shorter wavelengths of the ultraviolet spectrum, generally those shorter vantages of our invention will appear from the following detailed description.

In the drawing, Fig. 1 shows a sunlamp of a type commonly in use constructed in accordance than '280 mu, and yet transmit with as little energy loss a possible the medium and longer wavelengths. -These shorter wavelength radiations have generally harmful efiects'which are difiicult to guard'against in the absence of professional supervision. v

Although glasses possessing such transmission characteristicsare known, most of them undergo some change in their spectral transmission characteristicslduring the operating life of the lamp while in some the change is very great. The result is that the same lamp may causequite difierent biologic effects at different times during its operating life. Under such circumstances the user can rely neither upon the tables of exposure furnished with the lamp nor upon. his experience with previous exposures. Neither can he rely upon the sensation during exposure a an indication of radiation intensity since the ultraviolet radiation generallybecomes noticeable only after several hours.

These undesirable aging phenomena may be suppressed'by the addition of small amounts of nickel oxide to a bulb of alkali-silicate glass in the manner described in United States Patent No. 2,212,879 issued August 27, 1940, to Harry Kalsing et al. By the present invention,'however, we have not only obtained this desired result but also a spectral transmission characteristic curve of much more favorable shape.

It is therefore an object of our invention not only to avoid the uncertainty caused by the changing spectral character of the radiation from ultraviolet sunlamps by maintaining the spectral analysis of the lamp radiation constant during the entire life of the lamp but also to obtain, at the sametime, a particularly advantageous transmission characteristic. This object is accomplished according to ourinvention by employing a bulb of alkali-silicate glass which contains from to of lead oxide along with a silica content of more than 60%. Further objects and adwith our invention while Fig. 2 shows a typical spectral transmission curve of a glas made in accordance with our invention.

Referring more particularly to Fig. 1, the enveloping bulb 2, provided with a conventional threaded base i similar to that of an incandescent lamp, contains a spherical high pressure mercury lamp 3 and a coiled incandescent filament l, which serves as a series resistance for limitin the discharge current. Lamp 3 is preferably constructed of a high melting point, ultraviolet transmitting glass, especially quartz glass, and

ignitiongas, a drop of mercury 6. The size of the mercury drop is so chosen that during operation of the lamp an unsaturated vapor pressure of about 100 atmospheres is developed whereby the arc voltage rises to about 130 to 140 volts. The high pressure tube will then 'consumeabout 65 to 70 watts with a specific wall loading of its inner surface of more than 30 watts per square centimeter. The sunlamp may be connectedto any convenient source of power with a voltage of the order of 220 or more and may have a power consumption of about 110 watts with an operating current of about 0.5 ampere. The series resistor 4 is preferably designed as an incandesce t filament and not only serves to limit the discharge current but also furnishes additional radiation, especially heat radiation. Alternatively, the lamp 3 may be of the type disclosed in the United States Patent No. 2,094,694 to Cor'nelis Bol et a1. or any ofthe high pressure mercury vapor type designed to operate at pressures from.

to preferably 72% $102 10 to 15%, preferably 11.5% K20 4 to 8%, preferably 6% NazO 0 to 5%, preferably 0.5% A1203 5 to 15%, preferably 10% PhD The alkali content of the glass of morethan 12% facilitates in a familiar manner the melting and also the working of the glass.

Where a small design of enclosing bulb 2 is desirable, it maybe necessary to take into consideration a high temperature rise during the lamp operation. In that case, a lead oxide hard glass of the following composition may be used advantageously:

The transmission characteristics of enclosing bulbs of these compositions are very favorable. The spectral transmission curve is substantially flatter than those of glasses heretofore known and extends considerably into the short wave region before substantially complete cut-off btains at about 250 mu. With the customary bulb wall thicknesses of about 0.5 to 1.0 millimeters, the absorption of wave lengths below 280 mu is practically complete. For example, with a bulb wall thickness of 0.7 mm. and a glass of the firstmentioned composition at the preferred proportions, we obtain the particularly sharp cut-oil characteristic curve shown in Fig. 2 wherein relative energy transmission eillciencies are plotted as a function of wavelength.

As indicated by the curve itself, radiation below the wavelength 280 mu (millimicrons) is substantially absorbed and rendered harmless to the body, while at only slightly higher wavelengths of about 310 mu the transmission has reached a value of 80% of the total. This is particularly advantageous since it is the ultraviolet radiations above this approximate cut off range which are desirable for the purposes of sunlamps.

Sunlamps of the type shown can be used in the usual sockets of incandescent lamps without external series resistance and can be used by laymen for home exposure without danger. They have, in addition, the advantage that the quality of the spectral radiation remains constant throughout the operating life.

For improving the color tone of the lamp radiation or the appearance of the lamp or for more or less strongly absorbing the visible radiation, coloring matters may be added in the manner well known in the art. For example, cobalt oxide, nickel oxide or manganese oxide may be used. If a small amount of antimony monoxide or bismuth oxide is added to the bulb glass, these will function as substitutes for the lead oxide. Small amounts of these ingredients will permit a relatively largereduction of the lead oxide content. Of course, the bulb glass must be sumciently free of such materials or impurities as iron oxide which diminish the transmission of ultraviolet radiation.

It will be understood that the herein described glass may be used to advantage with many typ s of sunlamps; that the particular lamp herein described is illustrative of but one embodiment of our invention andis not to be construed as a limitation upon the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An ultraviolet transmitting glass, impervious to ultraviolet radiations of wavelengths short. or than about 280 mu and having a substantially constant ultraviolet transmission characteristic, containing 72% SiOz, 11.5% K20, 6% NazO, 0.5% A1203, and 10% PhD.

2. An ultraviolet transmitting glass, impervious to ultraviolet radiations of wavelengths shorter than about 280 mu and having a substantially constant ultraviolet transmission characteristic, containing 69.0% SiOa, 17.0% B203, 1.2% AlzOa, 1.1% SbzOs, 1.7% Nero, 4.0% K20, 5.7% PhD and aszoi. 

